fix(distribution): 货架加价打通前台、下单与卖方分成

分站公开列表和详情展示当前货架加价；下单写入 base_price / shelf_markup / markup_site_id 快照并计入实付。
支付分账改用快照加价，不再误用 PlatformFeeCent；结账不退加价，事后改价不影响历史订单。

backend/internal/modules/order/repository_test.go

@@ -118,6 +118,35 @@ func TestBuildOrderPricingDoesNotDiscountAllExtraItemOrder(t *testing.T) {
 	}
 }
 
+func TestCheckoutDoesNotRefundShelfMarkup(t *testing.T) {
+	order := model.RentalOrder{
+		RentAmountCent:      20000,
+		OwnerRentAmountCent: 8000,
+		PlatformFeeCent:     2000,
+		BasePriceCent:       10000,
+		ShelfMarkupCent:     10000,
+		DepositAmountCent:   1000,
+		AccountSnapshot: datatypes.JSON([]byte(`{
+			"haf_coin_amount": 100000000,
+			"asset_summary": {
+				"price_breakdown": {
+					"buyer_coin_base_price": 100,
+					"seller_coin_base_price": 80,
+					"consumable_price": 0
+				}
+			}
+		}`)),
+	}
+	settlement := calculateCheckoutSettlement(order, 0, 100, 0)
+	if settlement.RentRefundCent != 0 {
+		t.Fatalf("full consume must not refund shelf markup, rent refund = %d", settlement.RentRefundCent)
+	}
+	zeroUse := calculateCheckoutSettlement(order, 0, 0, 0)
+	if zeroUse.RentRefundCent != 10000 {
+		t.Fatalf("unused listing refunds base price only, got %d want 10000", zeroUse.RentRefundCent)
+	}
+}
+
 func TestCalculateCheckoutSettlementRefundsUnusedRent(t *testing.T) {
 	order := model.RentalOrder{
 		RentAmountCent:      38300,
@@ -527,4 +556,3 @@ func TestApplyAdminOrderFiltersSmartRouting(t *testing.T) {
 		})
 	}
 }
-